This invention relates to surgical dressings and in particular to the covering of a wound, lesion or the like with an adherent film to effect protection therefor during the healing process.
A very large number of people are seriously burned in domestic and industrial accidents every year, and the number of these victims which die in spite of intensive medical care is distressingly high. In Canada, the number of burn injuries requiring hospital admission approaches 25,000 per year. In the United States, about 130,000 are hospitalized annually because of burns; of these, 70,000 require intensive care at a cost exceeding $300,000,000., and 10,000 die.
The problem of burn treatment is even more acute in areas of the world in which there is armed conflict, since many of the weapons of modern warfare either directly or indirectly cause burns to both military personnel and civilians. In time of war the demands on medical facilities and supplies are very severe, and the mortality rate among burn victims is greatly increased.
In a third degree burn, the full thickness of the skin has been destroyed. The complete absence of "skin" cells in the burned area means that a new covering of skin will not spontaneously form there except by the very slow proliferation of healthy cells at the edges of the burn. One treatment is to remove a thin sheet of healthy skin from the patient's own body and graft it on to the burned area. Only a partial thickness of skin is removed, so that the cells in the remaining layer of skin can regenerate a full thickness in the area from which the graft was harvested. In cases of burns covering 50% or more of the body surface area, this grafting procedure will be a lengthy process carried out in several stages because of the time required for regeneration of skin on the harvested sites.
In the intervening period between hospitalization and grafting, two very serious problems are caused by the absence of skin in the area of the burn. One of the most important functions of normal skin is to restrict the loss of body water by evaporation. The dramatic increase in water loss caused by destruction of the skin produces a large rate of heat loss due to the cooling effect of evaporation. In order to maintain a normal body temperature, the metabolic rate must increase, and a rapid depletion of fat and protein reserves ensues. The other serious problem caused by the absence of skin is bacterial invasion. If this invasive infection is not restricted, the high bacteria population makes the wound unsuitable for skin grafting. The victim of a major burn who receives no treatment for this infection will ultimately die from it.
After removal of the layer of dead tissue (eschar) lying on top of the burned area, it is desirable to cover the wound with a dressing which will control water loss and assist the body's own defences in controlling bacterial proliferation until skin grafting can be carried out.
Two natural materials, pigskin and human skin from cadavers, are regarded as very effective burn dressings. These materials can, under favourable circumstances, adhere to the wound very well and effectively control water loss and infection. The problem is that the body recognizes these biological materials as foreign substances, and begins a cellular response to reject them. Because of this, these biological dressings must be replaced every 2 to 4 days. The other major drawback of these materials is their high cost. Cadaver skin $80. and up per square foot, and pig skin at about $30. per square foot, are so expensive that physicians can be reluctant to use them except in cases in which they are essential for survival of the patient.
The disadvantages associated with these biological materials have given rise to the preparation of a large number of synthetic substitutes. The more effective of these have consisted of a foam, velour, or fibrous mat laminated to a synthetic resin film. Adhesion to the wound occurs by growth of tissue into the interstices of the foam or fibres, and the film controls loss of body water and prevents entry of bacteria. This basic approach has some inherent drawbacks. Since the adhesion depends on ingrowth, some time must elapse before the dressing is firmly adherent to the wound. A more serious problem in many cases has been the tenacious adherence that eventually does take place. Removal of the dressing can then be a traumatic procedure which may produce excessive bleeding and leave fragments of the synthetic material in the wound. These fragments may delay the healing of the wound when skin grafting is carried out.
Two laminates of this type are on the market. One of these, a laminate of microporous polypropylene reticulated polyurethane foam is sold under the trademark EPIGARD by Parke, Davis and Co. For a variety of reasons, EPIGARD has not been widely accepted for clinical use by surgeons who treat burn patients. The other laminate is sold under the trademark BIOBRANE by Hall-Woodroof Inc. It is a composite of a flexible nylon fabric and an ultra-thin silicone rubber membrane. The high cost of BIOBRANE is a very serious drawback which may limit its acceptance.
A radically different type of burn dressing has been developed by I. V. Yannas and J. F. Burke and co-workers in the United States. Their approach has been to produce a material which slowly biodegrades at the wound surface and is assimilated by the body. During this biodegradation, the dressing not only restricts water loss and controls infection, but also acts as a tissue culture medium. Ultimately, migration of epidermal cells forms a new skin over the wound site. At the present state of development of their film, the healing of only relatively small wounds by this elegant process is possible. The film can be used to advantage on large wounds, but skin grafting is still required at a later stage. A commercial form of the film, when available, will probably be quite expensive.
In U.S. Pat. No. 3,164,560 which issued Jan. 5, 1965, John F. Suter teaches the use of a gelatin/polyalkylene oxide composition in the form of continuous films of improved extensibility and flexibility as compared to gelatin films and which have improved tensile strength and toughness as compared to polyalkylene oxide films. The films are used, for example, in packaging and photographic supplies. There is no teaching or suggestion of use as wound dressings.
U.S. Pat. No. 4,265,233 of May 5, 1981 in the name of Sugitachi et al teaches a material for the healing of wounds having blood coagulation Factor XIII fixed thereto. A wide variety of polymers including gelatin and other polymers, such as poly(ethylene oxide) and polyethylenimine, are specified as useful materials. It is emphasized that this type of dressing operates on the basis of the formation of stabilized fibrin at the wound site. The materials are preferably body absorbable. Moreover, any materials of which blood coagulation Factor XIII is a significant component would be expected to be very expensive. It is also emphasized that this teaching in no way teaches or suggests the use of combinations of gelatin and other polymers.
It is therefore an object of my invention to fill the need for an effective yet inexpensive wound dressing.
It is a further object of my invention to provide a burn wound-adherent dressing material which forms a naturally wound-adherent covering over the burn wound which controls water-loss and minimizes ingress of exogeneous micro-organisms during the healing process or until it is removed to permit skin grafting.